For forming containers, films, sheets and the like, melt molding using a resin composition is generally employed. Such a resin composition is desired to be capable of forming articles having less defects such as streaks and fish eyes and having superior appearance characteristics, and to be superior in properties for operation over a long time period (long-run workability), i.e., properties that the defects are less likely to be generated even in melt molding over a long time period, and the like. In particular, such defects not only deteriorate the appearance of the formed articles but also cause deterioration of performance; therefore, inhibition of the generation of defects is important.
On the other hand, ethylene-vinyl alcohol copolymers (hereinafter, may be also referred to as “EVOH(s)”) are polymeric materials that are superior in gas barrier properties against oxygen and the like, oil resistance, antistatic properties, mechanical strength, and the like. Thus, EVOH-containing resin compositions have been widely used as forming materials of formed articles such as containers.
However, since EVOH has a comparatively active hydroxyl group in its molecule, an oxidization reaction and a crosslinking reaction are caused in a molten state at high temperatures even in the interior of an extrusion molding machine in a state being almost free from oxygen, and thus thermal deterioration products may be generated. In particular, when a continuous operation is carried out over a long time period, the thermal deterioration products are likely to be deposited in the forming machine, leading to occurrence of gelation that accounts for fish eyes. Thus, insufficient long-run workability tends to be caused in the melt molding using the EVOH-containing resin composition.
In order to overcome such disadvantages, a variety of EVOH-containing resin compositions have been developed. For example, an EVOH-containing resin composition that exhibits improved long-run workability during the melt molding due to containing a boron compound, sodium acetate and magnesium acetate (see Japanese Unexamined Patent Application, Publication No. H11-60874), an EVOH-containing resin composition that inhibits the occurrence of gelation on melt molding due to containing a conjugated polyene compound (see Japanese Unexamined Patent Application, Publication No. H9-71620), an EVOH-containing resin composition that is superior in thermal stability and exhibits inhibited oxidative gel formation at elevated temperatures due to containing a specific carboxylic acid metal salt and a hindered phenol antioxidant (see Japanese Unexamined Patent Application, Publication No. H4-227744), and the like have been developed.
However, according to these conventional EVOH-containing resin compositions, the improvement of the long-run workability is unsatisfactory, and additionally, when a large amount of the metal salt is contained in the resin composition, the formed article tends to be yellowed, leading to an unfavorable appearance. Moreover, in consideration of the environment, for example, in light of a reduction in amounts of basic materials and waste of formed articles such as packaging materials, a reduction in thickness of the formed articles has been desired. Such a reduction in thickness is likely to be accompanied by the unfavorable appearance, and therefore a further improvement of the appearance has been needed. Additionally, an odor in molding must be taken into consideration from an environmental viewpoint.